Estimating rock properties using sound signal dominant frequencies during diamond core drilling operations

In many engineering applications such as mining,geotechnical and petroleum industries,drilling operation is widely used.The drilling operation produces sound by-product,which could be helpful for preliminary estimation of the rock properties.Nevertheless,determination of rock properties is very difficult by the conventional methods in terms of high accuracy,and thus it is expensive and timeconsuming.In this context,a new technique was developed based on the estimation of rock properties using dominant frequencies from sound pressure level generated during diamond core drilling operations.First,sound pressure level was recorded and sound signals of these sound frequencies were analyzed using fast Fourier transform (FFT).Rock drilling experiments were performed on five different types of rock samples using computer numerical control (CNC) drilling machine BMV 45 T20.Using simple linear regression analysis,mathematical equations were developed for various rock properties,i.e.uniaxial compressive strength,Brazilian tensile strength,density,and dominant frequencies of sound pressure level.The developed models can be utilized at early stage of design to predict rock properties.

An automatic loading system for rock core testing with an industrial CT scanner

A new type of a loading and measuring system was developed for testing failure and deformation of rock core samples with an industrial CT （ICT） scanner.The loading and measuring system consisted of a loading system and a computer control system.The maximum servo-controlled force was 2 tonnes.The new system was a high-stiffness system with a small size.During ICT tests,rock core samples could be easily loaded in the axial direction.So the initiation,propagation,and coalescence of cracks in core samples were observed on ICT images.

Core discing characteristics and mitigation approach by a novel developed drill bit in deep rocks

Core discing often occurs in deep rocks under high-stress conditions and has been identified as an important characteristic for deep rock engineering.This paper presents the formation mechanism of core discing firstly.Then,the interaction between diamond drill bits and rock was analyzed based on numerical modeling.A novel drill bit with an inner conical crown for the mitigation of core discing was designed and verified by simulation experiments.The mitigation method was applied in the cavern B1 of CJPL-Ⅱand satisfactory results had been achieved.The percentage of core discing had been obviously decreased from 67.8%when drilling with a rectangular crown drill bit,to 26.5%when an inner conical crown drill bit had been adopted.This paper gives full insight into core discing characteristics and provides a new method for core discing mitigation;it will potentially contribute to stress measurement in deep rock engineering.

Relationship between rock uniaxial compressive strength and digital core drilling parameters and its forecast method

The rock uniaxial compressive strength(UCS)is the basic parameter for support designs in underground engineering.In particular,the rock UCS should be obtained rapidly for underground engineering with complex geological conditions,such as soft rock,fracture areas,and high stress,to adjust the excavation and support plan and ensure construction safety.To solve the problem of obtaining real-time rock UCS at engineering sites,a rock UCS forecast idea is proposed using digital core drilling.The digital core drilling tests and uniaxial compression tests are performed based on the developed rock mass digital drilling system.The results indicate that the drilling parameters are highly responsive to the rock UCS.Based on the cutting and fracture characteristics of the rock digital core drilling,the mechanical analysis of rock cutting provides the digital core drilling strength,and a quantitative relationship model(CDP-UCS model)for the digital core drilling parameters and rock UCS is established.Thus,the digital core drilling-based rock UCS forecast method is proposed to provide a theoretical basis for continuous and quick testing of the surrounding rock UCS.

Rock magnetic property of gravity core CSH1 from the northern Okinawa Trough and the effect of early diagenesis

Detailed rock magnetic investigations were undertaken at 2 -4 cm interval for the gravity core CSHI （with a length of 17.36 m） from the northern Okinawa Trough. Time-scale of the core was constructed by two characteristic tephras and foraminferal assemblages, indicating an age of 50 ka for the bottom of the core. Except for three tephras and abrupt decrease in surface, there are little changes in all kinds of rock magnetic parameters that can be correlated to the climate change for the last 50 ka. Different from the common sediments, most S-ratios （S equals the negative ratio of IRM-0.3T to SIRM, which is an indicator of low coercivity content） of the sediments are smaller than 0. 9, which implies a substantial amount of magnetic minerals with high coercivity. The existence of iron sulphide （ greigite or pyrrhotite） is revealed by representative susceptibility - temperature curves showing 200 350 ℃ Curie temperature in addition to 580 ℃ of magnetite, and also by awful smell during heating and dark heating products. Both the occurrence of authigenic iron sulphide and quick decrease of magnetic parameters near the surface clearly show that sediments from Core CSHI have undergone early diagenesis. The featureless magnetic changes of the whole core except for three tephras mean that the post-depositonal alteration is so strong that most original signals have been destroyed. For the same reason, the organic matter in sediment and sulphate in pore water must have been consumed along with dissolution, precipitation of iron and manganese happening sequencially during the redox reaction series. Great caution must be taken when using these altered chemical parameters for the interpretation of climatic changes.

Experimental and Theoretical Investigation of Wave Forces on APartially-Perforated Caisson Breakwater with A Rock-Filled Core

The total horizontal and vertical forces acting on a partially-perforated caisson breakwater and their phase difference are investigated in this study. The perforated breakwater sits on the rubble tilled foundation, and has a rock-filled core. An analytical solution is developed based on the eigenfunction expansion and matching method to solve the wave field around the breakwater. The finite element method is used for simulating the wave-induced tlow in the rabble-filled foundation. Experiments are also conducted to study the wave forces on the perforated caissons. Numerical predictions of the present model are compared with experimental resuhs. The phase differences between the total horizontal and vertical forces are particularly analyzed by means of experimental and numerical results. The major factors that affect the wave forces are examined.

Pore-based architecture and representative element volume evaluation in artificial sand packs and natural rock cores

The phenomenon of multiphase flow in porous media is confronted in various fields of science and industrial applications. Owing to the complicated porous structure, the flow mechanisms are still not completely resolved. A critical and fundamental question is the variation of pore structure and REV sizes among different types of porous media. In this study, a total of 22 porous samples were employed to systematically evaluate the pore-based architecture and REV sizes based on X-ray CT image analysis and pore network modelling. It is found that the irregular grain shapes give rise to large specific areas,narrow and thin throats in identical sand packs. The packs with more types of sands, or composited by the sands with larger difference in diameter, have larger specific area, smaller tortuosity and pore spaces.Based on the REV measurement through porosity solely, the REV sizes of sand packs are generally in the order of magnitude of 10^(-2) m L, while it is at least one order of magnitude smaller in rock cores. Our result indicates that the combination of porosity and Euler number is an effective indicator to get the REV sizes of porous samples.

Determination of mining-induced stresses using diametral rock core deformations

Knowledge of ground stresses is crucial for ground control activities such as the design of underground openings,selec-tion of support systems,and analysis for stability.However,it is a known fact that far field stresses experience changes in orientation and magnitude due to the presence of geological structures and due to the excavations created by mining activi-ties.As a result,in-situ stresses around drifts,ramps,and stopes in underground mines are quite different from far field or pre-mining stresses.The purpose of this research is to develop a simple and practical methodology for determining in-situ stresses.Stress relief occurs once the rock core is drilled off.Such relief is a function of the surrounding stress field.This study uses exploration rock cores that are drilled off for the purpose of orebody definition in the underground mine.The method measures and analyzes the diametral core deformations in laboratory.Two case studies from operating underground mines are presented for demonstration.In these case studies,rock core deformations are measured with a customized test apparatus and rock samples were prepared and tested for Young's modulus and Poisson's ratio.The differential stress,namely the difference between the local principal stresses in the plane perpendicular to the core rock axis is calculated.It is shown that this methodology is useful for determining the brittle shear ratio in the rock mass,which is of primary interest to ground control studies.

Growth behavior and resource potential evaluation of gas hydrate in core fractures in Qilian Mountain permafrost area, Qinghai-Tibet Plateau

The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment,due to its well-developed fractures and abundant gas sources.Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area.The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area.The formation and distribution characteristics of multi-component gas hydrates in core samples were observed in situ by X-ray Computed Tomography(X-CT)under high pressure and low temperature conditions.Results show that hydrates are mainly formed and distributed in the fractures with good connectivity.The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8%and 60.67%in two different core samples.This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples.Based on the field geological data and the experimental results,it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×1013 m3,with a resource abundance of 8.67×108 m3/km2.This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.

沥青混凝土心墙堆石坝心墙拱效应研究

心墙拱效应是影响土石坝安全稳定运行的重要因素,心墙力学特性复杂且受众多因素的影响,复杂地形地质条件对心墙拱效应具有重要影响。首先对比了直心墙、斜心墙、下直上斜式心墙拱效应的差异,在此基础上选取岸坡坡度、河谷宽度、覆盖层厚度以表征坝体所处的地形地质条件。基于数值计算定量研究复杂地质条件对沥青混凝土心墙拱效应的影响规律。结果表明:心墙应力拱效应主要集中在心墙中部3/4坝高附近及靠近岸坡处;斜心墙应力拱效应相对较小,可以很好地改善心墙的整体受力状况;岸坡变陡,斜心墙整体的拱效应强度增加,应力传递的核心区域由心墙中部拓宽至心墙两岸坡;随着河谷宽度的增加,应力传递的重心逐渐由底部转移到心墙两岸及心墙中上部;斜心墙整体的应力拱效应并非随着河谷宽度的增加单调变化,当坝轴线长度与坝高比值增加到3~4时,河谷产生的河谷效应对斜心墙变形及拱效应的影响大幅下降;随着覆盖层厚度的增加,斜心墙底部的拱效应明显增强,底部的拱效应系数分布逐渐集中化、区域化,容易产生局部破坏。

伽马能谱测井在罗辛铀矿勘查中的应用研究

纳米比亚罗辛铀矿床属于白岗岩铀-钍混合型矿床。在一定量矿心分析数据对比基础上,一直沿用γ测井解释结果作为铀资源储量估算的基础数据。针对该伽马测井结果,要经过各种校正,尤其是钍作为一种“干扰”的不可忽视的因素。大量(岩)矿心分析历史数据表明,罗辛铀矿床Th/U比随着矿体走向、倾向以及深度、蚀变、岩性的变化而变化;通过数理统计分析矿心Th/U比采用常数法或者函数拟合方法用于γ测井的钍修正。但利用伽马能谱测井方法可直接获取矿(化)段的铀、钍元素含量。从仪器、数据采集、误差分析、伽马能谱测井解释铀含量与钍修正后γ测井解释铀含量,以及与矿心分析元素含量对比等几方面进行论述,验证该方法的可靠性和可信度。结果表明,伽马能谱测井是一种快速、有效的测井方法,尤其适用于热液型铀矿勘查。

框架-分布双段摇摆芯筒-核心筒体系调谐减震机理及性能研究

为了减小传统框架-核心筒(FCT)结构体系筒体围合面积,进一步提高结构的经济性,提出框架-分布芯筒-核心筒(FDCT)高层结构体系;将分布芯筒与摇摆体系相结合形成框架-分布摇摆芯筒-核心筒(FDRCT)结构体系,旨在控制结构的变形模式。为了降低高阶振型对高层结构的不利影响,进一步提出具有调谐减震性能的框架-分布双段摇摆芯筒-核心筒(FDBRCT)结构体系。建立各结构的动力学模型和方程,并进行平稳随机振动分析,初步证明FDBRCT结构可以更为有效地降低结构的动力响应。对比FCT,FDCT,FDRCT以及FDBRCT结构的时程分析结果,FDCT结构由于刚度被削弱导致抗震能力下降,FDRCT改善了结构变形的不均匀程度,上部楼层加速度有所减小但顶层位移会增大。相较于FDRCT结构,FDBRCT结构的层间位移角最大值明显减小,变形更加均匀,适当降低了顶层位移响应以及内力需求,具备调谐能力的分布双段摇摆芯筒使FDBRCT结构在提高经济性的同时兼具更为优越的抗震、减震性能。

中空螺杆马达井底动力绳索取心钻具的研制与试验

针对大洋钻探硬岩取心钻具钻进效率低、取心效率低等问题,本文介绍了中国地质科学院勘探技术研究所研制的Ø185 mm规格中空螺杆马达井底动力绳索取心钻具的基本研制情况及陆地试验情况。研制过程中,通过理论计算和Ansys Workbench有限元仿真模拟,对中空式螺杆马达螺旋线型的结构进行了优化设计及动力学分析,并对万向节进行了受力安全分析,优选了材质,钻具攻克了多头小偏移量短节距中空转子和柔性中空万向节等关键技术,通过在陆地开展花岗岩块取心试验,验证了该取心钻具原理样机工作性能的可行性,为该钻具的工程应用提供了工作参数指导及匹配钻头的优选,也可为我国大洋钻探及深地科学钻探提供硬岩取心技术支持。

深井高速涡轮钻配套同径取心技术研究

分析了涡轮钻具结构特征及性能特点,在深井、特深井的高温高压、强研磨性地层中,涡轮钻具基本上成为唯一可选的用于复合钻进提速降本的井下动力钻具。针对深部资源的勘探开发需求,阐述了现有涡轮钻具同径取心技术的优势及存在的问题,利用数值模拟仿真技术分析和研究了涡轮钻具同径取心过程中钻井液的流动状态对取心效果的影响,认识到涡轮钻具可耐高温,适于深井、特深井全面钻进及取心钻进,但其高转速在取心钻进过程也容易造成岩心磨损、岩柱螺旋,而改善同径取心钻具高速单动性能、加长涡轮钻具螺旋稳定器、利用反螺旋扰流板等技术措施,有利于减小取心钻具井底的涡动、降低岩心内外管轴向速度差,从而提高涡轮钻同径取心钻进的岩心质量。

基于钻井岩屑评价水平井地层力学性质——以鄂尔多斯盆地太原组灰岩为例

鄂尔多斯盆地太原组致密灰岩气藏储层开发潜力高,规模化开发建产依赖于分段体积压裂技术。水平井井段取心难度大、成本高,难以获取全井段力学性质以支撑压裂方案精细优化,但全井段钻井岩屑可轻易获取。文章创新性地提出了一种基于钻井岩屑评价水平井地层力学性质的方法。通过开展井下岩心的单轴/三轴压缩实验和纳米压痕测试,明确灰岩的微观组分模型,研究单一组分响应与宏观整体响应的关系。针对同井同深度的钻井岩屑和井下岩心开展网格化纳米压痕测试,标定钻井岩屑与井下岩心力学性质的关系,基于钻井岩屑建立水平井地层力学性质连续剖面。应用实例表明,基于钻井岩屑的纳米压痕测试,有利于精细化表征水平井地层岩性和连续反演水平井地层的静态弹性模量分布,为水平井地层压裂甜点识别、压裂段簇及射孔优化提供基础数据。研究结果证明了基于钻井岩屑表征地层岩石力学性质的可行性,为水平井全井段储层力学性质剖面的建立提供新思路,有助于水平井密切割压裂方案的精细优化。

基于数字岩心的碳酸盐岩复杂孔隙特征研究——以普光气田飞仙关组储层为例

川东北普光气田飞仙关组为一套深层海相碳酸盐岩储层,储集空间类型、组合方式多样,孔隙结构复杂,储层非均质性强,利用常规测井资料难以有效表征其储层的孔隙结构及渗透力。文中应用数字岩心技术精细刻画孔隙结构,即采用全直径岩心CT扫描、微米级X-ray CT扫描、大面积扫描电镜拼图成像技术等,建立纳米—厘米级别的多维度多尺度的岩心数字化表征。对大数据图像特征参数提取和分析,建立了不同类型储层的孔渗关系,将整个储层类型分为三区一带:微裂缝区、粒(晶)间孔主控区、铸模孔区、粒间孔加铸模孔过渡带。研究明确了粒(晶)间孔结构是渗透率的主控因素,更好地明确了该类储层孔隙结构对渗流能力的影响,揭示了礁滩相碳酸盐岩地层的微观渗流特性。

页岩数字岩心重构与水力压裂数值试验

为了实现对深部页岩油储层水力裂缝扩展规律的精细研究,以吉木萨尔凹陷芦草沟组陆相页岩油储层下甜点主要油层段为研究对象,对3684.62~3705.70 m深度范围内的20组页岩样品进行扫描并构建数字岩心,开展水力压裂数值试验.试验获得了各模型的破裂压力和水力裂缝扩展路径.结果表明:破裂压力随孔隙度的增加而降低,随着脆性矿物体积分数的增加而增加,和石英体积分数呈现较明显的线性关系.水力裂缝在孔隙位置起裂,连通独立的孔隙区域并沿着贯通的孔隙区域继续扩展.在远离孔隙区域时,水力裂缝主要沿垂直于最小主应力方向延伸.水力裂缝的复杂程度均随石英体积分数和孔隙度的增加而增加,但也会受到矿物分布形态的影响.当石英体积分数或孔隙度较高且呈现大面积连通分布时,水力裂缝的扩展受到抑制,水力压裂的增渗改造效果较弱.

易碎煤岩制备方法及其孔渗参数测试技术

由于煤岩脆性强,结理、裂缝发育,难以制备为标准柱塞,导致其常规孔渗实验难以展开。采用岩心浇筑技术,建立了一种非柱塞状煤岩孔隙度、渗透率测定方法,将易碎煤岩切割成长方体后,利用环氧树脂胶将长方体煤岩塑型成圆柱状,并进行孔隙度、渗透率测试分析。实验结果表明:当煤岩岩心截面积制备成25mm×25mm长方体时,与柱塞状岩心测试的孔隙度、渗透率具有较好的相关性,孔隙度相关系数达到了0.922 1,渗透率相关系数达到了0.954 3。从而解决了煤岩易碎岩心不能满足实验设备测试的需求,为储层物性参数提供了有力的支撑。

Changes in filtration and capacitance properties of highly porous reservoir in underground gas storage:CT-based and geomechanical modeling

The paper presents the results of comprehensive studies of filtration and capacitance properties of highly porous reservoir rocks of the aquifer of an underground gas storage facility.The geomechanical part of the research included studying the dependence of rock permeability on the stress-strain state in the vicinity of the wells,and physical modeling of the implementation of the method of increasing the permeability of the wellbore zone-the method of directional unloading of the reservoir.The digital part of the research included computed tomography(CT)-based computer analysis of the internal structure,pore space characteristics,and filtration properties before and after the tests.According to the results of physical modeling of deformation and filtration processes,it is found that the permeability of rocks before fracture depends on the stress-strain state insignificantly,and this influence is reversible.However,when downhole pressure reaches 7-8 MPa,macrocracks in the rock begin to grow,accompanied by irreversible permeability increase.Porosity,geodesic tortuosity and permeability values were obtained based on digital studies and numerical modeling.A weak degree of transversal anisotropy of the filtration properties of rocks was detected.Based on the analysis of pore size distribution,pressure field and flow velocities,high homogeneity and connectivity of the rock pore space is shown.The absence of pronounced changes in pore space characteristics and pore permeability after non-uniform triaxial loading rocks was shown.On the basis of geometrical analysis of pore space,the reasons for weak permeability anisotropy were identified.The filtration-capacitance properties obtained from the digital analysis showed very good agreement with the results of field and laboratory measurements.The physical modeling has confirmed the efficiency of application of the directional unloading method for the reservoir under study.The necessary parameters of its application were calculated:bottomhole geometry,stage of operation,stresses and pressure drawdown value.

高土石坝心墙砾石土料掺配施工技术

高砾石土心墙土石坝防渗体砾石土料的质量对坝体结构稳定和长期安全运行至关重要,通过对不同土料掺配施工技术研究,制定出精确掺配的相关施工工艺参数,解决了常规施工存在的诸多问题,提高了高土石坝砾石土料掺拌和填筑施工质量,节约了工程施工成本,确保了坝体结构稳定和运行安全,为工程正常有序施工及完建创造了良好的条件。